The present invention relates to a rod-bed assembly and to be more precise to a rod-bed assembly for a rod of a device for coating or sizing a fiber web, particularly a paper or a board web, having a holder, an insert removably and insertably supported in a groove of the holder and the insert having a recess for a rod to be rotatably supported in the recess.
In this description and the claims by the term rod-bed assembly is meant the rod-bed comprising an insert and a holder. The rod-bed assembly is used for a rod of a device for coating or sizing a fiber web and the front side of a rod-bed assembly is the side on which the rod is located in use, i.e. the side that will face the fiber web to be coated or the sizing roll onto which the sizing agent is applied by the rod when sized. It should be noted that in prior art publications relating to rod-bed assemblies there are differences in the terminology used, for example in relation to the feature whether or not the rod is included in the assembly. In practice the rods and the rod-bed assemblies can be supplied to a device for coating or sizing a fiber web from different suppliers or from the same supplier.
As known from the prior art, fiber web producing processes typically comprise an assembly formed by a number of apparatuses arranged consecutively in the process line. A typical production and treatment line comprises a head box, a wire section and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise other devices and sections for finishing the fiber web, for example, a sizer, a coating section and a calendar. The production and treatment line also comprises at least one winder for forming customer rolls as well as a roll packaging apparatus. In this description and the following claims by fiber webs are meant for example paper and board webs.
In production of fiber webs, for example of paper or board webs, sizing is used to alter the properties of a fiber web by adding sizing agents (sizing medium), for example glue chemicals. Sizing can be divided into internal sizing and surface sizing. In internal sizing the sizing agent is added to pulp in the wet end of the fiber web machine before forming. In surface sizing the sizing agent is added onto the surface of the fiber web at the dry end of the fiber web machine.
In the production of fiber webs, for example of paper or board webs, coating, especially the surface of a fiber web is formed with a layer of coating paste (coating medium) at a coating station followed by drying. The coating process can be divided in supplying the coating paste onto the web surface, which is called the application of the coating paste, as well as in the adjustment of the final amount of coating paste.
The coating or the sizing of a fiber web typically utilizes a coating device—a coater—or a sizing device—a sizer. In connection with the coaters and sizers different kinds of application technology for application of the coating or the sizing medium on the fiber web are employed in prior art arrangements, for example curtain technology or blade coating technology or rod coating technology or air brush coating technology or spray coating technology.
In the coating or sizing based on rod technology, rod-bed assemblies are used for the rod or doctor rod functioning as dosing and/or coating elements of the coating or sizing medium for applying the coating or sizing medium and/or scraping off the excessive medium quantity of the sizing or coating medium. In the sizing, the rod functions against a roll and in the coating the rod functions against the fiber web.
DE 100 45 515 A1 shows one example of a known rod-bed assembly which comprises a holder, a doctor bed made of elastic material inserted into the holder for rods. EP 1 485 209 A1 shows a further example of a known rod-bed assembly in which a metal doctor rod is insertable into a rod-bed made of elastomer. The rod-bed insert is inserted into a holding groove of a holder also made of elastomer. EP 1 954 880 A1 shows yet a further example of a known rod-bed assembly in which the rod cradle (the rod-bed) includes a frame profile (holder) equipped with an insert groove, an insert fitted to this equipped with a rod groove and a rod and locking elements for locking the insert into the frame profile. WO 2010/142513 shows also an example of a known rod-bed assembly comprising a holder made of composite material, a rod-bed made of polymer and a doctor rod rotatably supported in a bearing recess on the front side of the rod-bed. The holder is formed such that the rod-bed and the doctor rod are insertable into and removable from a socket provided in the holder in the radial direction of the rod, and the rod-bed comprises closed cavities for saving material.
Typically the holder of the rod-bed assembly is made of extruded polymer or composite material and the insert of the rod-bed assembly is made of extruded polymer, for example of extruded polyethene. The holder is made of a profile that is massive and rigid. Furthermore, the groove for the insert in the holder must be stiff in order to keep the fitting of the rod when located and in order to facilitate the use of cost effective materials for the insert manufacture. The typical C-shape of the groove further stiffens the profile.
It is a problem of the prior art that in the rod-bed assemblies the rigidity of the holder prevents cross-directional profiling in dosing sizing or coating medium. By cross-directional profiling is meant the profiling in the cross-direction of the fiber web to be sized or coated in relation to the running direction of the fiber web.